Rotating field sensor

Abstract

A first detection unit has first and second detection circuits. A second detection unit has third and fourth detection circuits. Output signals of the second and fourth detection circuits differ from output signals of the first and third detection circuits in phase, respectively, by an odd number of times ¼ the signal period. The output signal of the third detection circuit differs from the output signal of the first detection circuit in phase by an integer multiple of ⅙ the signal period other than an integer multiple of ½ the signal period. A rotating field sensor generates a first signal based on the output signals of the first and third detection circuits, generates a second signal based on the output signals of the second and fourth detection circuits, and calculates a detected angle value based on the first and second signals.

What is claimed is: 
     
       1. A rotating field sensor for detecting an angle that a direction of a rotating magnetic field in a reference position forms with respect to a reference direction, the rotating field sensor comprising:
 a first detection unit that detects the rotating magnetic field in a first position; and 
 a second detection unit that detects the rotating magnetic field in a second position, wherein: 
 the first detection unit has a first detection circuit that detects an intensity of a component of the rotating magnetic field in a first direction and outputs a signal indicating the intensity, and a second detection circuit that detects an intensity of a component of the rotating magnetic field in a second direction and outputs a signal indicating the intensity; 
 the second detection unit has a third detection circuit that detects an intensity of a component of the rotating magnetic field in a third direction and outputs a signal indicating the intensity, and a fourth detection circuit that detects an intensity of a component of the rotating magnetic field in a fourth direction and outputs a signal indicating the intensity; 
 each of the first to fourth detection circuits includes at least one magnetic detection element; 
 the output signals of the first to fourth detection circuits make periodic changes with one signal period; 
 the output signals of the first to fourth detection circuits are all distorted from an ideal sinusoidal curve to a shape between the ideal sinusoidal curve and a triangular waveform, or all distorted from the ideal sinusoidal curve to a shape between the ideal sinusoidal curve and a rectangular waveform; 
 the output signal of the third detection circuit differs from the output signal of the first detection circuit in phase; and 
 the output signal of the fourth detection circuit differs from the output signal of the second detection circuit in phase, 
 the rotating field sensor further comprising: 
 a first arithmetic circuit that generates, based on the output signals of the first and third detection circuits, a first signal having a correspondence relationship with both the intensity of the component of the rotating magnetic field in the first direction and the intensity of the component of the rotating magnetic field in the third direction, the first signal including a reduced error component with a period of ⅓ the one signal period, as compared with the output signals of the first and third detection circuits; 
 a second arithmetic circuit that generates, based on the output signals of the second and fourth detection circuits, a second signal having a correspondence relationship with both the intensity of the component of the rotating magnetic field in the second direction and the intensity of the component of the rotating magnetic field in the fourth direction, the second signal including a reduced error component with a period of ⅓ the one signal period, as compared with the output signals of the second and fourth detection circuits; and 
 a third arithmetic circuit that calculates, based on the first and second signals, a detected angle value having a correspondence relationship with the angle that the direction of the rotating magnetic field in the reference position forms with respect to the reference direction. 
 
     
     
       2. The rotating field sensor according to  claim 1 , wherein:
 the output signal of the second detection circuit differs from the output signal of the first detection circuit in phase by an odd number of times ¼ the one signal period; 
 the output signal of the third detection circuit differs from the output signal of the first detection circuit in phase by an integer multiple of ⅙ the one signal period other than an integer multiple of ½ the one signal period; and 
 the output signal of the fourth detection circuit differs from the output signal of the third detection circuit in phase by an odd number of times ¼ the one signal period. 
 
     
     
       3. The rotating field sensor according to  claim 2 , wherein the first position and the second position are identical with each other in the direction of rotation of the rotating magnetic field, and the first direction and the third direction are different from each other in the direction of rotation of the rotating magnetic field by a spatial angle equivalent to an integer multiple of ⅙ the one signal period other than an integer multiple of ½ the one signal period. 
     
     
       4. The rotating field sensor according to  claim 2 , wherein the first position and the second position are different from each other, and the difference between the first position and the second position is equivalent to an integer multiple of 1/6  the one signal period other than an integer multiple of ½ the one signal period. 
     
     
       5. The rotating field sensor according to  claim 1 , wherein each of the first to fourth detection circuits includes, as the at least one magnetic detection element, a pair of magnetic detection elements connected in series. 
     
     
       6. The rotating field sensor according to  claim 5 , wherein each of the first to fourth detection circuits has a Wheatstone bridge circuit that includes a first pair of magnetic detection elements connected in series and a second pair of magnetic detection elements connected in series. 
     
     
       7. The rotating field sensor according to  claim 5 , wherein the magnetic detection elements are magnetoresistive elements. 
     
     
       8. The rotating field sensor according to  claim 7 , wherein each of the magnetoresistive elements has a magnetization pinned layer whose direction of magnetization is pinned, a free layer whose direction of magnetization varies according to the direction of the rotating magnetic field, and a nonmagnetic layer disposed between the magnetization pinned layer and the free layer. 
     
     
       9. The rotating field sensor according to  claim 8 , wherein:
 the directions of magnetization of the magnetization pinned layers of the magnetoresistive elements in the second detection circuit are orthogonal to those of the magnetization pinned layers of the magnetoresistive elements in the first detection circuit; and 
 the directions of magnetization of the magnetization pinned layers of the magnetoresistive elements in the fourth detection circuit are orthogonal to those of the magnetization pinned layers of the magnetoresistive elements in the third detection circuit. 
 
     
     
       10. The rotating field sensor according to  claim 1 , further comprising:
 a third detection unit that detects the rotating magnetic field in a third position; and 
 a fourth detection unit that detects the rotating magnetic field in a fourth position, wherein: 
 the third detection unit has a fifth detection circuit that detects an intensity of a component of the rotating magnetic field in a fifth direction and outputs a signal indicating the intensity, and a sixth detection circuit that detects an intensity of a component of the rotating magnetic field in a sixth direction and outputs a signal indicating the intensity; 
 the fourth detection unit has a seventh detection circuit that detects an intensity of a component of the rotating magnetic field in a seventh direction and outputs a signal indicating the intensity, and an eighth detection circuit that detects an intensity of a component of the rotating magnetic field in an eighth direction and outputs a signal indicating the intensity; 
 each of the fifth to eighth detection circuits includes at least one magnetic detection element; 
 the output signals of the first to eighth detection circuits make periodic changes with the one signal period; 
 the output signal of the seventh detection circuit differs from the output signal of the fifth detection circuit in phase; and 
 the output signal of the eighth detection circuit differs from the output signal of the sixth detection circuit in phase, 
 the rotating field sensor further comprising: 
 a fourth arithmetic circuit that generates, based on the output signals of the fifth and seventh detection circuits, a third signal having a correspondence relationship with both the intensity of the component of the rotating magnetic field in the fifth direction and the intensity of the component of the rotating magnetic field in the seventh direction, the third signal including a reduced error component with a period of ⅓ the one signal period, as compared with the output signals of the fifth and seventh detection circuits; 
 a fifth arithmetic circuit that generates, based on the output signals of the sixth and eighth detection circuits, a fourth signal having a correspondence relationship with both the intensity of the component of the rotating magnetic field in the sixth direction and the intensity of the component of the rotating magnetic field in the eighth direction, the fourth signal including a reduced error component with a period of ⅓ the one signal period, as compared with the output signals of the sixth and eighth detection circuits; 
 a sixth arithmetic circuit that calculates, based on the third and fourth signals, a second detected angle value having a correspondence relationship with the angle that the direction of the rotating magnetic field in the reference position forms with respect to the reference direction; and 
 a seventh arithmetic circuit that calculates a detected value of the angle that the direction of the rotating magnetic field in the reference position forms with respect to the reference direction, based on a first detected angle value, which is the detected angle value calculated by the third arithmetic circuit, and the second detected angle value calculated by the sixth arithmetic circuit. 
 
     
     
       11. The rotating field sensor according to  claim 10 , wherein:
 the output signal of the second detection circuit differs from the output signal of the first detection circuit in phase by an odd number of times ¼ the one signal period; 
 the output signal of the third detection circuit differs from the output signal of the first detection circuit in phase by an integer multiple of ⅙ the one signal period other than an integer multiple of ½ the one signal period; 
 the output signal of the fourth detection circuit differs from the output signal of the third detection circuit in phase by an odd number of times ¼ the one signal period; 
 the output signal of the sixth detection circuit differs from the output signal of the fifth detection circuit in phase by an odd number of times ¼ the one signal period; 
 the output signal of the seventh detection circuit differs from the output signal of the fifth detection circuit in phase by an integer multiple of ⅙ the one signal period other than an integer multiple of ½ the one signal period; and 
 the output signal of the eighth detection circuit differs from the output signal of the seventh detection circuit in phase by an odd number of times ¼ the one signal period. 
 
     
     
       12. The rotating field sensor according to  claim 10 , wherein:
 the first detected angle value includes a first angular error with respect to a theoretical value of the first detected angle value that is expected when the direction of the rotating magnetic field rotates ideally; 
 the second detected angle value includes a second angular error with respect to a theoretical value of the second detected angle value that is expected when the direction of the rotating magnetic field rotates ideally; 
 the first and second angular errors make periodic changes with the same angular error period in response to a change of the direction of the rotating magnetic field, the changes of the first angular error and the second angular error depending on the change of the direction of the rotating magnetic field; and 
 the third position and the fourth position are offset from the first position and the second position, respectively, by an amount equivalent to an odd number of times ½ the angular error period. 
 
     
     
       13. The rotating field sensor according to  claim 12 , wherein the angular error period is ½ the period of the rotation of the direction of the rotating magnetic field.